As a challenge required in line with the recent improvement in performance of semiconductor devices, how to package a high wattage multi-in/out device and also how to shorten a wire length between the device and a mother board have come to a technical aim. Besides, it is another theme how to achieve the above aim at a low cost, including process cost, with high reliability. As countermeasures to these problems, a cavity-fill formed PPGA or PBGA having a structure shown in FIG. 5 is proposed. Namely, a substrate 2 comprising a multi-layer circuit with a center hole is put on a metallic heat sink 1. Then, a semiconductor element 3 is incorporated within a cavity formed with the metallic heat sink 1 and the substrate 2, which is encapsulated with a resin layer 4. In FIG. 5, 9 are conductive globular bumps. As a method of encapsulating a semiconductor element, a method of encapsulating by covering a cavity with a ceramic board may be listed in addition to the above encapsulating method using the resin layer.
The sealing method using a ceramic board has some problems. The problems are; high cost of ceramic and incomplete sealing caused in bonding a ceramic board on a substrate to seal a cavity, because the bonding ability between organic materials, for example, a substrate or a bonding agent, and an inorganic material, for example, a ceramic board is inferior, resulting in a decrease in this sealing method one time. Meanwhile, in the encapsulating method by forming the encapsulating resin layer 4 to encapsulate the semiconductor element 3 (FIG. 5), a liquid resin composition is usually employed as a material for forming the encapsulating resin layer 4, which is formed by injecting the liquid resin composition into the cavity. However, when the liquid resin composition is employed, it should be stored at an extremely low temperature (about -40.degree. C. ). Also, since the liquid resin composition must be injected into a suitable position with a suitable amount by using an injector, special apparatus are required to control these conditions. Further, to obtain high fluidity, a liquid material with low moisture-proof reliability or a material containing solvent, which requires low-temperature preheating in curing, is employed, causing a lot of problems in relation to process reliability. Besides, in order to improve fluidity, a material with low content of a filler is employed, wherein a linear expansion coefficient becomes higher and greatly different from that of a semiconductor element, a substrate, a heat sink or the like, resulting in a problem that stress is applied when using.